A just-received GMI overpass indicates that Sergio has become betterorganized with formation of a well-defined eye and eyewall under aconvective overcast with cloud tops to -85C. Satellite intensityestimates are in the 55-65 kt range, and based on the improvedstructure, the intensity will be set at the upper end of that range.Thus, Sergio is upgraded to a hurricane.

The intensity forecast is low confidence. The better structure ofSergio is now conducive for rapid intensification. However, thelarge-scale models forecast northeasterly vertical shear to increaseto 20-25 kt by 24 h, which should be strong enough to stop rapiddevelopment, although the guidance suggests at least slowstrengthening during this time. The intensity forecast follows theguidance trend in calling for gradual strengthening, but there couldbe a 12-h or so burst of rapid intensification before the shear getstoo strong. The shear should subside after about 36 h while Sergiois still over warm water, and the forecast shows the system becominga major hurricane near the 72 h point in response to the morefavorable conditions. After 72 h, a combination of decreasingsea-surface temperatures along the forecast track and entrainment ofdrier air should lead to gradual weakening.

The initial motion is 265/12. As stated in the previous discussion,a westward motion at about the same forward speed is expected duringthe next day or so while the storm remains on the south side of amid-level ridge. A turn to the west-northwest is forecast by lateTuesday, followed by a northwestward motion on Wednesday as thewestern portion of the mid-level ridge erodes due to a large scalemid- to upper-level trough near the southwestern United States. Bythe end of the forecast period, a ridge is expected to build to thenorth of Sergio, which should cause a turn back toward the west. Thetrack guidance has changed little since the last advisory, and thenew NHC track is close to both the previous forecast track and theconsensus models.

The above post and any post by Ntxw is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including Storm2k. For official information, please refer to NWS products.

Geostationary satellite imagery indicates that Sergio continues tostrengthen. The center is located within a fairly symmetric CDOwith cloud tops of -70 to -80 degrees C. Earlier microwave datashowed a well-defined eye and inner core, but a more recent AMSUoverpass suggests that there has been some slight erosion of theeastern portion of the eye, possibly due to some intrusion of drymid-level air. Dvorak intensity estimates ranged from 75 to 90 kt,and the initial intensity has been increased to a possibilityconservative 75 kt for this advisory.

The intensity forecast remains somewhat uncertain. AlthoughSergio has developed an inner core and strengthened during the past12 hour or so, the dynamical models suggest northeasterly shearwill increase over the hurricane today. This is expected to temperthe intensification somewhat over the next 12-24 hours, however,most of the guidance shows at least gradual strengthening duringthe next day or so. The NHC intensity forecast calls for a gradualincrease in wind speed over the next 36-48 hours, and is close tothe IVCN model consensus. After 72 h, cooler waters and theentrainment of drier air is expected to cause gradual weakening.

Sergio is moving slightly south of due west or 265/12 kt. Thehurricane is currently located to the south of a mid-level ridge,and Sergio should continue westward today. The global models showthe western portion of the ridge weakening over the next severaldays, which should cause Sergio to turn west-northwestward, thennorthwestward on Wednesday. By late in the week, another ridgeis predicted to build to the northwest of Sergio and the hurricaneis forecast to turn back toward the west. The overall guidanceenvelope has changed little this cycle, and the new NHC track issimilar to the previous advisory and close to the various consensusaids.

Could Sergio join the Pacific wide Cat 5 party in the next 1 to 3 days?

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Here comes the eye. Easily will be the 9th major and 9th Cat 4 for the EPAC. He will have to keep those cloud tops very cold for a 5 given the conservative nature of the agencies these days.

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The cloud pattern of Sergio continues to become better organized onsatellite imagery. The hurricane has a very cold cloud-toppedcentral dense overcast, with a developing eye, surrounded by curvedbanding features. The current intensity is set at 85 kt based on ablend of subjective and objective Dvorak estimates. Sergio isforecast to continue moving over warm waters, under moderatevertical shear and within a moist mid-level airmass for the nextfew days. Therefore, additional strengthening is likely, and Sergiowill probably become a major hurricane in a day or so. The officialintensity forecast is close to the latest model consensus, IVCN.

The hurricane has been moving westward at a slightly slower pace,and the motion estimate is 270/11 kt. A mid-level ridge to thenorth of the system will soon be eroding, due to a trough droppingin from the northwest. This change in steering currents shouldresult in Sergio turning toward the west-northwest today followedby a northwestward motion in 2-3 days. In the latter part of theforecast period, the ridge builds back in, and this is likely tocause the tropical cyclone to turn back toward the west. The NHCtrack forecast is similar to the previous one and follows thedynamical model consensus, TVCN, fairly closely.

Sergio has intensified significantly today. The eye of thehurricane has become better defined, and is embedded in very coldconvective cloud tops. Outer banding features are also welldefined. Upper-tropospheric outflow is strong over the western andsouthern portions of the circulation, and a little restricted tothe northeast. The advisory intensity is set, probablyconservatively, to 100 kt in agreement with a Dvorak estimate fromSAB. Only modest northeasterly shear is expected to affect Sergioover the next few days. That, along with warm waters and a verymoist middle troposphere, should be conducive for furtherstrengthening. The official forecast is near the upper end of theintensity guidance model suite.

The system continues moving mostly westward, or 280/11 kt. Thereis little change to the track forecast reasoning from the previouscouple of advisory packages. A mid-level ridge to the north ofSergio should weaken within the next 12 to 24 hours as a broadtrough drops in from the northwest. These changes in the steeringflow should cause the hurricane to turn toward the west-northwest bythis evening or tonight, and to begin moving northwestward onWednesday. The official track forecast is is very similar to theprevious one and, again, follows the latest multi-model consensus.

Some slight enlargements to the wind radii were made over theeastern semicircle of Sergio based on scatterometer data.

Sergio has pumped ~5 units of ACE so far. The NHC 5 day forecast yields an additional ~13 units. Euro has Sergio still around in 10 days.

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